Abstract: As a kind of metal-capture-agent,food grade tannic-acid(TA)was immobilized on commercial powdered activated carbon(PAC).Adsorption of low concentration Cr(Ⅵ)(0.500 mg·L^-1)on the TA-PAC was investigated at various dosage and pH,and adsorption capacities and adsorption isotherms were measured at 275 K.Compared with HNO₃- and NaOH-modified PAC(N-PAC and OH-PAC),the results obtained from the BET,Boehm’s titration and FTIR indicated that TA-PAC is of larger specific surface area,total pore volume and more abundant acid functional groups.The performance of TA-PAC,expressed by removal efficiency of Cr(Ⅵ)and total chromium,is much more excellent than N-PAC and OH-PAC.Its adsorption capacity for Cr(Ⅵ)was found to be pH-dependent,the removal efficiency both Cr(Ⅵ)and total chromium were notably higher in the acidic medium(pH=3.0-6.0)than in alkaline medium(pH=7.0-10.0).The adsorption data for total chromium were fitted using two-parameter isotherm models and the related parameters were estimated.Freundlich model is the best for data of C_e from 0.010 to 0.404 mg·L^-1,R²=0.9941,indicating a heterogeneous coverage of chromium on TA-PAC.Langmuir(Ⅰ),Langmuir(Ⅱ)and Temkin models didn’t fit the data well,because of occurring piecewise node at 0.149 mg·L^-1,0.151 mg·L^-1 and 0.163 mg·L^-1 respectively.The adsorption mechanism of TA-PAC for Cr(Ⅵ)was assumed to be chemical process,such as surface reduction of Cr(Ⅵ),esterification between chromate and catechol,and ion exchange.

Key words: PAC, hexavalent chromium, metal-capture-agent, food-grade tannic acid, surface modification

摘要： 针对低温微污染水中(275 K)低浓度Cr(Ⅵ)离子(0.500 mg·L^-1),制备基于表面负载食品级单宁酸为金属捕获剂的改性PAC(TA-PAC),以HNO₃、NaOH氧化改性PAC为对照,研究了TA-PAC的表面物理化学特性和吸附性能,并进行了pH影响和吸附等温线拟合研究。结果表明:TA-PAC的比表面积、总孔容积和表面极性大小最佳。TA-PAC对低温水中Cr(Ⅵ)及总铬的去除效果优于N-PAC和OH-PAC。酸性范围内(pH=3.0~6.0)TA-PAC对Cr(Ⅵ)及总铬的去除率均大于碱性范围(pH=7.0~10.0)。Freundlich 双参数吸附等温式对TA-HNC吸附水中低浓度总铬的吸附等温线拟合效果最好(R²=0.9941)。TA-PAC吸附低温水中低浓度Cr(Ⅵ)是一个极为复杂的过程,主要吸附机理可能包括表面还原作用、酯化/螯合作用和离子交换作用等。

关键词: 粉末活性炭, 六价铬, 金属捕获剂, 食品级单宁酸, 表面改性